The field of the invention is clear coats for use on the exterior of substrates. More specifically, the invention relates to coatings applied to the exterior of golf balls.
Clear coats are used on the exterior surfaces of a variety of substrates. Clear coats serve to enhance the aesthetic appearance of the substrate as well as act as a barrier to protect the substrate from weathering, mechanical agitation and the like. One such substrate in which clear coats are of particular importance is a golf ball.
A golf ball generally comprises a one-piece construction or it may include several layers including a core and an outer cover surrounding the core. Typically, one or more layers of paint and/or clearcoat are applied to the exterior surface of the golf ball. For example, in one typical design, the exterior surface of the golf ball is first painted with at least one clear or pigmented basecoat primer along with at least one application of a clear top coat. The basecoat and/or primer and clear top coat are applied to the golf ball to enhance the aesthetic appearance of the ball as well as mask or cover surface blemishes that may have resulted from the manufacturing process. The clear top coat is particularly important, in that the coat protects any markings, trademarks, logos, or the like that may be placed on the exterior surface of the ball.
Typically, the outer coating layers of a golf ball comprise a primer along with a clear urethane top coat. For example, U.S. Pat. No. 5,459,220 discloses a two-pack urethane top coat for a golf ball that uses separate packages of a polyol and diisocyanate that employs biurets and isocyanurate trimers of hexamethylene diisocyanate (HDI) as the crosslinking agents. U.S. Pat. No. 5,409,233 discloses a clear coating for use on a golf ball that incorporates a solvent system that includes methylamyl ketone (MAK).
Previous top coat formulations had the disadvantage that they were preferably used with the addition of a basecoat or primer. The elimination of the basecoat or primer is desirous, since the basecoat increases the cost of manufacturing as well as increases the production time of the golf ball. In addition, the primer or basecoat can be the source of volatile organic compounds (VOC's), that from an environmental standpoint, should be reduced or eliminated from the manufacturing process. Moreover, the presence of the primer coat can deleteriously affect the aerodynamic aspects of the golf ball during flight. The uneven distribution of primer over the cover as well as the pooling of primer within the dimples of the golf ball can alter the flight characteristics of the ball. In those instances where the top coat could be applied directly to the exterior of the cover, the cover had to meet specific chemical requirements such as a high zinc content, or favorable adhesion characteristics.
Consequently, there remains a need for a top coat that requires no basecoat or primer yet exhibits superior bonding to a variety of golf ball cover chemistries while still retaining superior abrasion resistance and durability.